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Fecal Coliform Bacteria TMDL and E. coli Revision- Rock Creek

Friday, January 9, 2015

On July 25, 2014, the US Environmental Protection Agency (EPA) approved the E. coli Total Maximum Daily Load (TMDL) for Rock Creek as a revision to the previous bacteria TMDL that was originally approved in 2004. The revision incorporates the new water quality standard for Escherichia coli (E. coli) that the District promulgated in October 2005. The load allocations specified in the original TMDL are still in effect; however, the revision provides a translation of those loads from fecal coliform to E. coli, which is the basis for the current bacteria water quality standard. A translator equation was developed from analysis of paired fecal coliform and E. coli sampling data collected from waters in the District. In addition to the translations to E. coli, the daily loading expressions for the new E. coli allocations are also provided.

The revision satisfies the requirements of the settlement agreement reached between EPA and Anacostia Riverkeeper, Friends of the Earth, and Potomac Riverkeeper (Case No.: 1:09-cv-00098-JDB of January 15, 2009) which stated that certain District TMDLs did not have a daily load expression established as required by Friends of the Earth vs. the Environmental Protection Agency, 446 F.3d 140, 144 (D.C. Cir. 2006). The settlement agreement requires the establishment of daily loads in District TMDLs by December 2014. The revisions are presented as an appendix to each existing watershed’s TMDL. They provide information and calculations regarding the translation from fecal coliform to E. coli, as well as methodologies for calculating the daily load expressions.